Fluoroscopic markers (markers which are clearly identifiable under fluoroscopy) have been used on tubular devices for various medical procedures to facilitate imaging and/or tracking a portion of the tubular member in a patient. This can assist a physician with delivery of the tubular device, which can be a catheter or the like.
For example, fluoroscopic markers have been used on catheters that are designed for delivering tubular prosthesis. Tubular prostheses such as stents, grafts, and stent-grafts (e.g., stents having an inner and/or outer covering comprising graft material and which may be referred to as covered stents) have been widely used in treating abnormalities in passageways in the human body. In vascular applications, these devices often are used to replace or bypass occluded, diseased or damaged blood vessels such as stenotic or aneurysmal vessels. For example, it is well known to use stent-grafts, which comprise biocompatible graft material (e.g., Dacron® or expanded polytetrafluoroethylene (ePTFE)) supported by a framework (e.g., one or more stent or stent-like structures), to treat or isolate aneurysms. The framework provides mechanical support and the graft material or liner provides a blood barrier.
Aneurysms generally involve abnormal widening of a duct or canal such as a blood vessel and generally appear in the form of a sac formed by the abnormal dilation of the duct or vessel. The abnormally dilated vessel has a wall that typically is weakened and susceptible to rupture. Aneurysms can occur in blood vessels such as in the abdominal aorta where the aneurysm generally extends below (distal to) the renal arteries or toward the iliac arteries.
In treating an aneurysm with a stent-graft, the stent-graft typically is placed so that one end of the stent-graft is situated proximally or upstream of the diseased portion of the vessel and the other end of the stent-graft is situated distally or downstream of the diseased portion of the vessel. In this manner, the stent-graft extends through the aneurysmal sac and spans and seals the proximal and distal ends thereof to replace or bypass the weakened portion. The graft material typically forms a blood impervious lumen to facilitate endovascular exclusion of the aneurysm.
Such prostheses can be implanted in an open surgical procedure or with a minimally invasive endovascular approach. Minimally invasive endovascular stent-graft use is preferred by many physicians over traditional open surgery techniques where the diseased vessel is surgically opened, and a graft is sutured into position bypassing the aneurysm. The endovascular approach, which has been used to deliver stents, grafts, and stent grafts, generally involves cutting through the skin to access a lumen of the vasculature. Alternatively, lumenar or vascular access may be achieved percutaneously via successive dilation at a less traumatic entry point. Once access is achieved, the stent-graft can be routed through the vasculature to the target site. For example, a stent-graft delivery catheter loaded with a stent-graft can be percutaneously introduced into the vasculature (e.g., into a femoral artery) and the stent-graft delivered endovascularly to a portion where it spans across the aneurysm where it is deployed.
When using a balloon expandable stent-graft, balloon catheters generally are used to expand the stent-graft after it is positioned at the target site. When, however, a self-expanding stent-graft is used, the stent-graft generally is radially compressed or folded and loaded into the distal end of a sheath or delivery catheter and self expands upon retraction or removal of the sheath at the target site. More specifically, a delivery catheter having coaxial inner and outer tubes arranged for relative axial movement therebetween can be used and loaded with a compressed self-expanding stent-graft. The stent-graft is positioned within the distal end of the outer tube (sheath) and in front of a stop fixed to distal end of the inner tube.
Regarding proximal and distal positions referenced herein, the proximal end of a prosthesis (e.g., stent-graft) is the end closest to the heart (by way of blood flow) whereas the distal end is the end furthest away from the heart during deployment. In contrast, the distal end of a catheter is usually identified as the end that is farthest from the operator, while the proximal end of the catheter is the end nearest the operator.
Once the catheter is positioned for deployment of the stent-graft at the target site, the inner tube is held stationary and the outer tube (sheath) withdrawn so that the stent-graft is gradually exposed and expands. An exemplary stent-graft delivery system is described in U.S. Patent Application Publication No. 2004/0093063, which published on May 13, 2004 to Wright et al. and is entitled Controlled Deployment Delivery System, the disclosure of which is hereby incorporated herein in its entirety by reference.
Although the endovascular approach is much less invasive, and usually requires less recovery time and involves less risk of complication as compared to open surgery, one challenge of this approach is positioning the catheter at the desired site. Fluoroscopic markers have been secured to catheters and the like to allow imaging and/or tracking of the catheter in a patient.
Radiopaque metal bands of fixed size have been attached to catheters and the like to provide a radiopaque marker to assist in locating the position of the catheter using conventional fluoroscopic techniques. These bands typically are not compressed onto the tubular catheter to secure it to the catheter as the band can wrinkle or kink, which can result in an undesirable increase in profile. Where wrinkling (or the presence of a raised portion on) the marker means the presence of a localized discontinuity greater than 0.0015 inches in the radius (0.003 inches in the diameter) of the marker measurable at a high or low point on the marker between adjacent marker band radiuses of substantially equal radial dimension such that the wrinkle (raised portion) is created when the marker ring is compressed from a first larger nominal diameter to a second smaller nominal diameter. Therefore, these fixed diameter bands generally must provide a close fit with the catheter and may need to be glued, crimped or pressed to the catheter to avoid slippage during multi step lamination of the catheter tube as it is constructed with an embedded marker. Other approaches have included, cutting a polymer tube that has been doped with radiopaque material to form a band that can be secured to the catheter or the like. The tube can be made by melting a polymer and adding metal powder so that the volume of metal is about 50 to about 75% of the volume of the tube. After a band is cut from the tube and placed over the catheter, it is bonded to the catheter with a laminate using heat treatment as is known. Alternatively, the band can be butt welded to the catheter with heat as is known. However, one drawback associated with using such a metal powder based ring is that the metal powder can cause degradation of the native polymer of the band and adversely impact its strength as it ages. Further, since the band is not pure metal, typically a thicker band is required to provide the same radiopacity as a metal band and this increases the profile of the device.
Accordingly, there remains a need to develop and/or improve fluoroscopic markers.